The invention relates to a blind rivet nut with pulling mandrel having a rivet tube with a flange, which is provided on its side remote from the flange with an internal thread extending from the end of the rivet tube via a portion of the rivet tube to a clinch zone of the rivet tube which is enlarged by means of a pulling mandrel fitting into the internal thread when the blind rivet nut is set, such that a workpiece receiving the blind rivet nut is clamped by the flange and the enlargement.
A blind rivet nut of this type is known from European Patent Application 158 304. For setting this blind rivet nut a particular pulling mandrel is used which pertains to the setting tool and is provided at its end extending into the internal thread of the blind rivet nut with an external thread fitting into the internal thread of the blind rivet nut and extending over the length thereof so that the pulling mandrel is capable of exerting a pulling force over the length of the internal thread on the rivet tube and of enlarging it in the region of its clinch zone. During the setting of the blind rivet nut, an opposing force is exerted on the flange of the rivet tube by a pressure piece penetrated by the pulling mandrel so that the force acting on the pulling mandrel can act fully on the clinch zone of the rivet tube, the pulling mandrel sliding, as during the setting of a conventional blind rivet, through the pressure piece formed by the setting tool during the setting of a conventional blind rivet. A workpiece, such for example as a sheet metal plate penetrated by the blind rivet nut, is clamped during this setting process so that the set blind rivet nut is therefore riveted. The workpiece is clamped between the flange of the rivet tube on the one hand and the enlargement of the rivet tube on the other hand. After the blind rivet nut has been set, the special pulling mandrel is screwed out of the blind rivet nut so that the blind rivet nut is available for screwing-in of a suitable bolt.
In addition, reference should also be made to German Gebrauchsmuster G90 01 069.8 relating to a blind rivet nut which is set by means of a fastening screw screwed into the blind rivet nut. The blind rivet nut is provided with a rivet tube of elastic material, more specifically rubber, into which a pipe provided with an internal thread is inserted. The pipe is rigidly connected to the rubber tube, for example by vulcanization. As the fastening screw is tightened, the rubber tube is compressed and forms a bead which is set behind the workpiece carrying the blind rivet nut, forming a clamp which consists, on the one hand, of the head and, on the other hand, of a flange closing the rubber tube. This blind rivet nut can be detached from its workpiece again when released by turning back the fastening screw and can therefore be used several times. Owing to the use of the elastic rubber tube, it does not form a rigid connection to the workpiece. Owing to the need to use an elastic rubber tube, this known blind rivet nut is not comparable to the blind rivet nut with pulling mandrel according to the invention. Furthermore, the known blind rivet nut has to be set by the tightening of the fastening screw, and the blind rivet nut is immediately detached from the workpiece carrying it when the fastening screw is loosened. Owing to this feature of the setting of the known blind rivet nut, the art forming the basis thereof follows a path deviating from the blind rivet nut according to the invention since the setting of a blind rivet nut with a pulling mandrel which remains freely rotatable in the blind rivet nut after the setting operation is not possible therewith owing to the special design of the know blind rivet nut. In this respect, therefore, there is a further fundamental difference between this blind rivet nut and the blind rivet nut with pulling mandrel according to the invention.
A voluminous prior art exists relating to blind rivet nuts. The embodiment described hereinbefore is to the fore and the same setting process is employed (see European Patent Applications 305868, 264870, U.S. Pat. Nos. 2,409,352, 3,948,142, 2,565,019, 3,461,771, GB-PS 1205744, DE-OS 3240539).
The object of the invention is to design a blind rivet nut with pulling mandrel so as substantially to simplify the processing thereof.